1. Field of the Invention
The present invention relates to an information storing medium, such as a magnetic disk or a magnetic tape, an optical disk, an optical card, or an optomagnetic disk, having information tracks for recording or reproducing information, and separate guide tracks for generating a tracking signal for performing tracking control. The present invention also relates to an information recording/reproducing apparatus for recording/reproducing information with respect to such an information storing medium, and to a tracking method using such an information storing medium.
2. Description of the Prior Art
FIG. 14 shows an example of the structure of a conventional magnetic tape serving as an information storing medium. Several series of information (three in FIG. 14) are recorded on this magnetic tape 601. These series of information are called information tracks 602. The spacing between an information track and its neighboring information track is called information track spacing, and is denoted as Tp. Guide tracks 603 for optical tracking control also are arranged on the magnetic tape 601. The spacing between a guide track 603 and its neighboring guide track 603 is called guide track spacing, and is denoted as Gp. On the guide tracks 603, grooves are arranged as tracking marks, having a suitable depth and width for being read optically.
There is a one-to-one correspondence between the guide tracks 603 and the information tracks 602, and the values for Tp and Gp are identical. Three light beams, emitted from an optical head, form three spots 701, 702 and 703 on the magnetic tape 601. The three spots 701, 702 and 703 are arranged obliquely with respect to the guide tracks 603 on the magnetic tape 601, and are irradiated at different positions in the Y-direction. The three light beams reflected from the magnetic tape 601 return to the optical head and enter a photo-detector. FIG. 15 is a circuit diagram showing a conventional example of obtaining a tracking signal. The photo-detectors 801, 802 and 803 receive the light beams 704, 705 and 706, and output a signal corresponding to the irradiated light amount. Here, the light beam 704 corresponds to the spot 701 on the magnetic tape 601, the light beam 705 corresponds to the spot 702, and the light beam 706 corresponds to the spot 703. The signals output from the photo-detectors 801 to 803 are sent to I-V amps 804 to 806, which give out a voltage signal. The signal given out by the I-V amp 804 is called S10, the signal given out by the I-V amp 805 is called SM0, and the signal given out by the I-V amp 806 is called S20. The differential amplifier circuit 807 receives the signals S10 and S20 and gives out a differential signal. The signal given out by the differential amplifier circuit 807 is the tracking signal, which is given out from a terminal 808.
This method for obtaining a tracking signal from the three light beams, is known as the three-beam method, for example in optical disk drives.
As shown in FIG. 3 of the present invention explained below, the optical head 300 and the magnetic head 301 lie on the same base and can be moved into the Y-direction of the magnetic tape with a transfer system 302. Based on the tracking signal obtained from the terminal 808, the magnetic head 301 performs a tracking control so that the magnetic head 301 is positioned above the information track 602 of the magnetic tape 601.
Recording/reproduction with other information tracks is performed by track jumping to different guide tracks.
A method for obtaining a tracking signal of high density with a conventional spot size is disclosed in Publication of Unexamined Japanese Patent Application (Tokkai) No. Hei 6-096453 (U.S. Pat. Nos. 5,406,545 and 5,650,987). In this method, the track spacing of the servo pattern region is twice the track spacing of the pit rows of the data region, two tracking signals with different phase are generated from the servo pattern region, and the product of the two tracking signals is calculated to obtain a tracking signal that is suitable for reproducing the pit rows of the data region. Consequently, the structure and the disclosed technological principle is different from the present invention. FIG. 5 of Tokkai Hei 6-096453 is structurally similar to the present invention, but the information tracks and guide tracks of the present invention are coplanar, so that its configuration is different from the present invention.
Tokkai Hei 6-052551 contains similar disclosures as Tokkai Hei 6-96453, but its configuration and principle are different from the present invention.
The track spacing of the guide tracks is determined by the spot size of the beams irradiated from the optical head. If the spot size is not made small, there is the problem that the track spacing of the information tracks cannot be made small, and it is not possible to raise the recording density.